This invention relates generally to digital data storage apparatus and more specifically to a digital storage apparatus employing a hard or "fixed" magnetic disk as a data storage medium. Still more specifically, the invention pertains to a system in such apparatus for reducing errors in reading data on such storage media.
In rotating magnetic disk apparatus in general, the individual bits of information are recorded on the disk as a pattern of reversals of magnetization. The transducer on scanning the disk produces a forward voltage for each forward or north seeking magnetization and a negative voltage for each reverse or south seeking magnetization, thereby providing one cycle of alternating current for each logic one. The transducer puts out no voltage for the logic zero since this is represented by unmagnetized regions on the disk. Such output from the transducer is amplified and directed into a read circuit, which reconstructs the recorded data by detecting the peaks of the transducer output waveform.
A problem has heretofore been encountered in thus reading data on the magnetic disk. Noise magnetizations are accidentally created on those parts of the disk track which should have been left unmagnetized to represent the logic zero, as well as on interblock gaps and any other gap between groups of signals on the disk. Conventionally, read errors occurred in such cases because the read circuit misconstrued such noise magnetizations as the logic one.